Wet strength resins are often added to paper and paperboard at the time of manufacture. In the absence of wet strength resins, paper normally retains only 3% to 5% of its strength after being wetted with water. However, paper made with wet strength resin generally retains at least 10%-50% of its strength when wet. Wet strength is useful in a wide variety of paper applications, some examples of which are toweling, milk and juice cartons, paper bags, and liner board for corrugated containers.
Dry strength is also a critical paper property, particularly in light of the recent trend for paper manufacturers to use high yield wood pulps in paper in order to achieve lower costs. These high yield wood pulps generally yield paper with significantly reduced strength when compared to paper made from highly refined pulps.
Commercially available wet strength resins include Kymene®557H, Kymene® 557LX, Kymene® SLX, Kymene® Plus, Kymene® 450 and Kymene® 736 wet strength resins, available from Hercules Incorporated, Wilmington, Del. Wet strength resins, such as those listed above, also provide increased dry strength to paper.
Resins similar to those used for imparting strength to paper are also often used as creping adhesives. In the manufacture of some paper products such as facial tissue, bathroom tissue, or paper towers, the paper web is conventionally subjected to a creping process in order to give it desirable textural characteristics, such as softness and bulk. The creping process typically involves adhering the web, a cellulose web in the case of paper, to a rotating creping cylinder, such as the apparatus known as a Yankee dryer, and then dislodging the adhered web with a doctor blade. The impact of the web against the doctor blade ruptures some of the fiber-to-fiber bonds within the web and causes the web to wrinkle or pucker.
The severity of this creping action is dependent upon a number of factors, including the degree of adhesion between the web and the surface of the creping cylinder. Greater adhesion causes increase softness, although generally with some loss of strength. In order to increase adhesion, a creping adhesive may be used to enhance any naturally occurring adhesion that the web may have due to its water content, which will vary widely depending on the extent to which the web has been previously dried. Creping adhesives should also prevent wear of the dryer surface and provide lubrication between the doctor blade and the dryer surface and reduce chemical corrosion, as well as controlling the extent of creping. A creping adhesive coating that adheres the sheet just tightly enough to the drum will give a good crepe, imparting absorbance and softness with the least possible loss of paper strength. If adhesion to the dryer drum is too strong, the sheet may pick or even “plug”, i.e., underride the doctor blade, and wrap around the dryer drum. If there is not enough adhesion, the sheet will lift off too easily and undergo too little creping.
The creping adhesive, usually as an aqueous solution or dispersion, is generally sprayed onto the surface of the creping cylinder or drun, e.g., a Yankee dryer. This improves heat transfer, allowing more efficient drying of the sheet. If the pulp furnish sticks too strongly to the creping cylinder, release agents can be sprayed on the cylinder. The release agents are typically hydrocarbon oils. These agents aid in the uniform release of the tissue web at the creping blade, and also lubricate and protect the blade from excessive wear.
Examples of creping adhesive compositions include those disclosed in U.S. Pat. No. 5,187,219 to Furman, which is incorporated by reference herein in its entirety. The compositions comprise water-soluble glyoxylated acrylamide/diallyldimethyl-ammonium chloride polymer and a water-soluble polyol having a molecular weight below 3000 as a plasticizer for the polymer.
U.S. Pat. No. 5,246,544 to Hollenberg et al., which is incorporated by reference herein in its entirety, discloses a reversibly crosslinked creping adhesive which contains a nonself-crosslinkable material that is a polymer or oligomer having functional groups that can be crosslinked by ionic crosslinking and at least one metal, cationic crosslinking agent having a valence of four or more. The adhesive can also contain additives to modify the mechanical properties of the crosslinked polymers, e.g., glycols, polyethylene glycols, and other polyols such as simple sugars and oligosaccharides.
Polyaminoamide/epichlorohydrin creping adhesives are disclosed in U.S. Pat. No. 5,338,807 to Espy et al., U.S. Pat. No. 5,994,449 to Maslanka, and Canadian Patent 979,579 Giles et al., which are incorporated by reference herein in their entireties.
U.S. Pat. No. 5,374,334 to Sommese et al., which is incorporated by reference herein in its entirety, discloses a creping adhesive which is a crosslinked vinyl amine/vinyl alcohol polymer containing from about 1 to about 99% vinyl amine. Epichlorohydrin is disclosed as a crosslinking agent.
U.S. Pat. Nos. 4,684,439 and 4,788,243 to Soerens, which are incorporated by reference herein in their entireties, disclose creping adhesives comprising mixtures of polyvinyl alcohol and water soluble thermoplastic polyamide resin comprising the reaction product of a polyalkylenepolyamine, a saturated aliphatic dibasic carboxylic acid and a poly(oxyethylene) diamine.
In U.S. Pat. Nos. 4,501,640 and 4,528,316 to Soerens, which are incorporated by reference herein in their entireties, there is disclosed a creping adhesive comprising a mixture of polyvinyl alcohol and a water soluble, thermosetting cationic polyamide resin.
Commercially available creping adhesives include Crepetrol® 190, Crepetrol® 290, and Crepetrol® 80E cationic polymers, available from Hercules Incorporated, Wilmington, Del.
Moreover, polyamine-epihalohydrin resins, such as polyaminopolyamide-epihalohydrin resins often contain large quantities of epihalohydrin hydrolysis products. For example, commercial polyaminopolyamide-epichlorohydrin resins typically contain 1-10 wt % (dry basis) of the epichlorohydrin (epi) by-products, 1,3-dichloropropanol (1,3-DCP), 2,3-dichloropropanol (2,3-DCP) and 3-chloropropanediol (CPD). Epi by-products are also known as epi residuals. Production of such resins with reduced levels of epi by-products has been the subject of much investigation. Environmental pressures to produce resins with lower levels of adsorbable organic halogen (AOX) species have been increasing. “AOX” refers to the adsorbable organic halogen content of the resin, which can be determined by means of adsorption onto carbon. AOX includes epichlorohydrin (epi) and epi by-products (1,3-dichloropropanol, 2,3-dichloropropanol and 3-chloropropanediol) as well as organic halogen bound to the polymer backbone.
Several ways of reducing the quantities of epihalohydrin hydrolysis products have been devised. Reduction in the quantity of epihalohydrin used in the synthetic step is an alternative taught in U.S. Pat. No. 5,171,795. A longer reaction time results. Control over the manufacturing process is taught in U.S. Pat. No. 5,017,642 to yield compositions of reduced concentration of hydrolysis products. These patents are incorporated by reference herein in their entireties.
Post-synthesis treatments are also taught. U.S. Pat. No. 5,256,727, which is incorporated by reference in its entirety, teaches that reacting the epihalohydrin and its hydrolysis products with dibasic phosphate salts or alkanolamines in equimolar proportions converts the chlorinated organic compounds into non-chlorinated species. To do this it is necessary to conduct a second reaction step for at least 3 hours, which adds significantly to costs and generates quantities of unwanted organic or inorganic materials in the wet strength composition. In compositions containing large amounts of epihalohydrin and epihalohydrin hydrolysis products (e.g., about 1-6% by weight of the composition), the amount of organic material formed is likewise present in undesirably large amounts.
U.S. Pat. No. 5,516,885 and WO 92/22601, which are incorporated by reference in their entireties, disclose that halogenated by-products can be removed from products containing high levels of halogenated by-products as well as low levels of halogenated by-products by the use of ion exchange resins. However, it is clear from the data presented that there are significant yield losses in wet strength composition and a reduction in wet strength effectiveness.
It is known that nitrogen-free organohalogen-containing compounds can be converted to a relatively harmless substance. For example, 1,3-dichloro-2-propanol, 3-chloro-1,2-propanediol (also known as 3-chloropropanediol, 3-monochloropropanediol, monochloropropanediol, chloropropanediol, CPD, 3-CPD, MCPD and 3-MCPD) and epichlorohydrin have been treated with alkali to produce glycerol.
The conversion of nitrogen-free organohalogen compounds with microorganisms containing a dehalogenase is also known. For example, C. E. Castro, et al. (“Biological Cleavage of Carbon-Halogen Bonds Metabolism of 3-Bromopropanol by Pseudomonas sp.”, Biochimica et Biophysica Acta, 100, 384-392, 1965), which is incorporated by reference in its entirety, describes the use of Pseudomonas sp. isolated from soil that metabolizes 3-bromopropanol in sequence to 3-bromopropionic acid, 3-hydroxypropionic acid and CO2.
Various U.S. patents also describe the use of microorganisms for dehalogenating halohydrins, eg., U.S. Pat. Nos. 4,452,894; 4,477,570; and 4,493,895. Each of these patents is hereby incorporated by reference as though set forth in full herein.
U.S. Pat. Nos. 5,470,742, 5,843,763 and 5,871,616, which are incorporated by reference herein in their entireties, disclose the use of microorganisms or enzymes derived from microorganisms to remove epihalohydrin and epihalohydrin hydrolysis products from wet strength compositions without reduction in wet strength effectiveness.
U.S. application Ser. No. 09/629,629, filed Jul. 31, 2000, which is incorporated by reference herein in its entirety, is directed to the use of microorganisms or enzymes derived from microorganisms to remove epihalohydrin and epihalohydrin hydrolysis products from resin compositions, and discloses a preferred sequential method for growth of the microorganisms.
Still further, U.S. Pat. No. 5,972,691 and WO 96/40967, which are incorporated by reference in their entireties, disclose the treatment of wet strength compositions with an inorganic base after the synthesis step (i.e., after the polymerization reaction to form the resin) has been completed and the resin has been stabilized at low pH, to reduce the organo halogen content of wet strength compositions (e.g., chlorinated hydrolysis products) to moderate levels (e.g., about 0.5% based on the weight of the composition). The composition so formed can then be treated with microorganisms or enzymes to economically produce wet strength compositions with very low levels of epihalohydrins and epihalohydrin hydrolysis products.
It is also known that epihalohydrin and epihalohydrin hydrolyzates can be reacted with bases to form chloride ion and polyhydric alcohols. U.S. Pat. No. 4,975,499 teaches the use of bases during the synthetic step to reduce organo chlorine contents of wet strength composition to moderate levels (e.g., to moderate levels of from about 0.11 to about 0.16%) based on the weight of the composition. U.S. Pat. No. 5,019,606 teaches reacting wet strength compositions with an organic or inorganic base. These patents are incorporated by reference in their entireties.
Moreover, U.S. application Ser. No. 09/001,787, filed Dec. 31, 1997, and Ser. No. 09/224,107, filed Dec. 22, 1998 to Riehle, and WO 99/33901, and which are incorporated by reference in their entireties, disclose amongst other features, a process for reducing the AOX content of a starting water-soluble wet-strength resin comprising azetidinium ions and tertiary aminohalohydrin, which includes treating the resin in aqueous solution with base to form treated resin, wherein at least about 20 mole % of the tertiary aminohalohydrin present in the starting resin is converted into epoxide and the level of azetidinium ion is substantially unchanged, and the effectiveness of the treated resin in imparting wet strength is at least about as great as that of the starting wet-strength resin.
Still further, U.S. patent application Ser. No. 09/592,681, filed Jun. 12, 2000, Ser. No. 09/363,224, filed Jul. 30, 1999, 09/330,200, filed Jun. 11, 1999, each of which is incorporated by reference in its entirety, are directed to polyamine-epihalohydrin resin products, particularly polyamine-epihalohydrin resin products which can be stored with at least reduced formation of halogen containing residuals, such as 3-chloropropanediol (CPD). Moreover, these applications disclose the use of microorganisms or enzymes derived from microorganisms to remove epihalohydrin and epihalohydrin hydrolysis products from wet strength compositions without reduction in wet strength effectiveness.
WO 99/09252 describes thermosetting wet strength resins prepared from end-capped polyaminoamide polymers. The endcappers used are monocarboxylic acids or monofunctional carboxylic esters, and are used to control the molecular weight of the polyaminamide in order to obtain wet strength resins with a high solids content.
Each of the foregoing approaches has provided various results, and there has been a continuing need for improvement in the use of polyamine-epihalohydrin resin, especially at high solids content. In particular, there is still a need for resin compositions, such as wet strength, dry strength and creping agent resins, that can be provided in solutions or dispersion of reasonable viscosity at relatively high polymer solids concentrations. Thus, there is still a need for resins that can be prepared, stored, treated and transported as a dispersion or solution containing high solids concentrations without product deterioration from polymer crosslinking, such as gelation problems.